1. Field of the Invention
The present invention relates generally to the field of sensor instruments, and more particularly relates to a sensor instrument system including methods for detecting analytes in fluids.
2. Description of the Prior Art
Sensor instruments are widely used in the technology of detecting analytes present in fluids. The following references are pertinent to this field of art:                1. U.S. Pat. No. 4,887,455 issued on Dec. 19, 1989 to Payne et al. for “Gas Sensor” (hereafter “the '455 Payne Patent”);        2. U.S. Pat. No. 5,571,401 issued on Nov. 5, 1996 to Lewis et al. for “Sensor Arrays for Detecting Analytes in Fluids” (hereafter “the '401 Lewis Patent”);        3. U.S. Pat. No. 6,319,724 issued on Nov. 20, 2001 to Lewis et al. for “Trace Level Detection of Analytes Using Artificial Olfactometry” (hereafter “the '724 Lewis Patent”);        4. Payne, et al., “High-Frequency Measurements of Conducting Polymers: Development of A New Technique for Sensing Volatile Chemicals”, Meas. Sci. Technol. 6 (1995) pp. 1500-1507 (hereafter “the Payne Publication”);        5. Nagle, H. T., et al., “The How And Why Of Electronic Nose”, IEEE Spectrum, September 1998, pp. 22-34 (hereafter “the Nagle Publication”);        6. Baltes, H., et al., “The Electronic Nose In Lilliput”, IEEE Spectrum, September 1998, pp. 35-38 (hereafter “the Baltes Publication”); and        7. U.S. Pat. No. 6,631,333 issued on Oct. 7, 2003 to Lewis et al. for “Methods For Remote Characterization Of An Odor” (hereafter “the '333 Lewis Patent”, in addition to U.S. Pat. No. 7,359,802 issued on Apr. 15, 2008 to the same inventors, which is a Divisional Patent of the '333 Lewis Patent); and        8. U.S. Pat. No. 7,465,425 issued on Dec. 16, 2008 to Sun for “Sensor And Method For Detecting Analytes In Fluids” (hereafter “the '425 Sun Patent”).        
The '455 Payne Patent discloses a gas sensor that has a semiconductor organic polymer layer exposed to a gas to be detected. An analyzer applies an alternating electric signal at specific resonant frequencies to the sensor to detect the change in the sensor's impedance characteristics which is compared by a microcomputer with reference characteristics stored in a memory of the microcomputer. The gas in contact with the sensor can be detected because of the resulting difference spectra. The patent further discloses that the best performance of the invention is likely to be conducted between frequencies ranging 100 MHZ to 500 MHZ where the resonance may happen.
The '401 Lewis Patent discloses arrays of chemical sensors, including polymer carbon powder based chemiresistor for detecting analytes in fluids. The sensors include first and second conductive elements electrically coupled to and separated by a chemically sensitive resistor which provides an electrical path between the conductive elements. The resistor includes a plurality of alternating nonconductive regions made of a nonconductive organic polymer and conductive regions made of a conductive material transverse to the electrical path. The resistor further provides a difference in resistance between the conductive elements when contacted with a fluid containing a chemical analyte at a first concentration, and then at a second different concentration. Arrays of such sensors are constructed with at least two sensors having different chemically sensitive resistors providing differences in resistance. Variability in chemical sensitivity from sensor to sensor is provided by qualitatively or quantitatively varying the composition of the conductive and/or nonconductive regions. An “electronic nose” for detecting an analyte in a fluid may be constructed by using such arrays in conjunction with an electrical measuring device electrically connected to the conductive elements of each sensor.
The '724 Lewis Patent discloses a method using artificial olfactometry for detecting the presence of an analyte indicative of various medical conditions, including halitosis, periodontal disease and other diseases.
The Payne Publication discloses the change in the alternating current (AC) impedance characteristics of poly-N-(2-pyridyl) pyrrole in the presence of different volatile chemicals.
The Nagle Publication is a special report, which summarizes research and development of the electronic nose instrument through 1990's. The report introduces in detail types of sensors including the respective sensing mechanisms for metal oxide thin film resistor sensors, conductive polymer sensors, polymer coated quartz crystal microbalance (QCM) sensors, polymer coated surface acoustic wave (SAW) sensors, metal-oxide-silicon field-effect-transistor (MOSFET) sensors, dye coated optical fiber (DCOF) sensors, gas chromatography (GC), light spectrum, and mass spectrometry (MS). The report also discloses advantages and disadvantages according to the respective sensors including the sensing mechanisms, wherein a high sensitivity to humidity is addressed as the disadvantage of the polymer film based sensors.
The Baltes Publication reports the developed micronose integrated circuit sensor CMOS chip coated with polymer films according to mechanisms of sensing mass change and dielectric constant change of the polymer films when they load up on volatile organic compounds.
The '333 Lewis Patent discloses compositions and systems useful in remote monitoring of chemical hazards, air quality and medical conditions. For example, robotic systems search for and detect explosives, mines, and hazardous chemicals. In addition, the methods, systems and compositions of the invention provide the ability to mine data from database containing a plurality of chemical fingerprints. The Patent also summarizes techniques for constructing sensors as disclosed in the Nagle Publication, in addition to a dye-impregnated bread (DIB) arrays and micromachined cantilver (MMC) arrays. The Patent further discloses the invented electrically conductive sensor that comprises alternating regions of a conductive material and a material compositionally different than the conductive material between two conductive leads wherein said sensor provides an electrical path through the regions of conductive material and the regions of the compositionally different material.
It can be seen from the above cited references that significant efforts have been devoted in the past in the research and development of sensor instrument systems, which is centered on the studying of sensors. This is because configuration of the sensors predominantly governs sensor instrument performance for detecting and identifying analytes in fluids. In instrument analysis, identification of analytes in fluids is accomplished through applying sensors which mimic mechanisms of the mammalian olfactory system that applies probabilistic repertoires of many different receptors to record a single odorant. Having such sensor technologies in conjunction with existing technologies in electrical engineering including highly integrated circuit chips (ICs), advanced softwares, remote data transmission, the current sensor instrument improves convenience in the analyte detection and identification.
It is well known that, from studying the mammalian olfactory system, identification of the odorant is dependent upon not only the results from highly specific receptors but also the output from less specific ones. In other words, identification is based on recognition a of a spectrum of signals that resemble a specific pattern. Following this direction, conventional technologies in sensor configuration are developed according to the following two schemes to generate a signal spectrum: applying strategies of a multiple sensor configuration and a single sensor configuration.
In the approaches that utilize the multiple sensor strategy, which are disclosed by the Nagle Publication in addition to the '333 Lewis Patent, various detecting devices have been developed that use metal oxide thin film resistor sensors, conductive polymer or polymer carbon powder composite film chemi-resistor sensors, QCM, SAW, MOSFET and DCOF sensors, and DIB and MMC arrays. However, although much progress has been made in the past, there are still primary disadvantages inherited from the sensing mechanisms of such multiple sensor technologies. The disadvantages include the requirement of a large number of sensors to generate a patterned information, the sophistication of the sensor configuration, thus the resulting poor reproducibility in sensor manufacturing, the strong humidity influence applying polymer film modified sensors on chemical analysis, the slow response, the expensive electronic equipment required, and the very restricted operating conditions.
Various polymer films with a general thickness of several micrometers have been extensively used in the multiple sensor strategy to improve sensor sensitivity and detection limit. This is primarily due to the fact that the polymer films can trap including adsorbing and absorbing analytes of chemicals, according to their specific chemical selectivities on the analytes. As a result, the analytes will be concentrated on the surfaces or inside of the polymer films prior to detection.
However, the conventional polymer films also inherit a number of disadvantages. First, the thin films of polymer are sensitive to the humidity associated with analytes. Humidity is the predominant factor to influence performance of the polymer film based gas sensors. Second, polymer films have an aging effect that affects the sensor stability for long term usages. Third, it is difficult to achieve reproducibility of the polymer films positioned in sensors, particularly in a situation when a large number of the sensors must be used according to the multiple sensor strategy.
In the approaches that utilize a single sensor strategy also disclosed by the Nagle Publication, various instruments have been developed that are based on the mechanisms of GC, MS, and light spectrum. Generally, these instruments are very expensive. Moreover, they are typically very bulky in size, which makes their miniaturization almost impossible. As a result, they are less attractive in the market, where portability of the instruments having wireless communication capabilities becomes increasingly important.
For example, a strategy of point-of-care (POC) is becoming an urgent demand in the field of medical diagnoses. Under the strategy POC, patient healthcare including medical diagnoses are directly conducted at the patients' bedsides of the respective patients' homes. Therefore, medical instruments are advantageous if they are completely portable. In addition, it is significantly advantageous if the instruments can have wireless and remote data communication capabilities, so that patients' health information can be in situ transmitted to a medical center for better patient treatment. In fact, instruments having portabilities and wireless communication capabilities are critical in many fields besides the medical field, including security, military and industrial fields.
As an example utilizing the single sensor strategy, the Payne Patent and Payne Publication discussed above disclose application of a single sensor for detecting the presence of gaseous analytes from detecting impedance and phase sensitive components of conductive polymer modified electrodes at specific frequencies, where electrical resonant signals are established due to interaction of analytes to the conductive polymer film. However, the Payne device requires high frequencies ranging from 100 MHZ to 500 MHZ, where the resonance may occur. The high frequency brings significant difficulties in instrument manufacturing and application. In addition, it still has the disadvantages inherent from polymer films.
In order to overcome deficiencies of the Payne technologies and invent a new single sensor applying frequency sweeping, the '425 Sun Patent discloses a single sensor as an analytical sensor for detecting analytes in fluids. The sensor is constructed from applying a pair of electrodes, wherein between the electrodes there are no additional materials designated to adsorb analytes if their concentrations are high, or there are adsorbents if the analyte concentrations are low. An alternating current voltage of varying frequencies is applied to the sensor by an alternating current device. In return, it detects electrical properties such as impedance and its components, reactance, resistance, and phase angles of the sensor with the analytes in fluids when they reside in or pass through the electrodes at each frequency. Thus two spectra of electrical properties of the analyte can be established at various applied frequencies from a single measurement. The electrical properties are analyzed by a pattern recognition process, and compared with those of the known objects. Therefore, the analyte can be detected and identified. A reference sensor is provided with the same configuration of the analytical sensor. By combining electrical properties from the analytical and reference sensors, the present invention provides a number of advantages, including elimination of humidity influence, polymer film aging effect, and electrical property variations caused by the temperature variations.
In the sensor instrument system development disclosed by the '333 Lewis Patent, a remote data processing function is combined with the sensor array including the carbon black polymer modified chemiresistors. Obviously, addition of the remote data processing is positive to the performance of the sensor instrument system.
However, in various situations, comprising a situation of testing air pollutants including ground level ozones in a regional environmental study, there is an additional need for a sensor instrument system which enables the sensor to provide information on variations of air pollutants in situ correlating to variations of geographic positions. Therefore, if satisfying the need, a regional pollutant distribution can be mapped for better understanding thus controlling the regional air qualities. Such capability of the sensor instrument system is also advantageous to many other studies.
Therefore, it is desirable to design and develop a new sensor instrument system including methods that overcomes the disadvantages of conventional sensor devices, and has a better reproducibility of performance and sensor manufacturing, fewer interference deficiency, enhanced sensitivity, less restricted operation conditions, and increased portability. In addition, the sensor instrument system will have wireless communication capabilities for processing data and abilities to locate geographic positions that associate with variations of the analyte information.